Components for applications at high temperatures consist of a superalloy with additional protection against oxidation, corrosion and high temperatures. To this end, the substrate of the component comprises a corrosion protection layer on which, for example, an outer ceramic thermal insulation layer is also applied.
Through-holes, out of which a coolant flows on the outer surface and contributes to the film cooling, are also made in the substrate and the layers for additional cooling. The film cooling hole is widened in the vicinity of the outer surface to form a so-called diffuser. When newly producing a component having a film cooling hole, problems arise since the diffuser must be made both through the layers and for the most part in the substrate. During the refurbishment of components, the problem is that the through-hole is already present and the substrate needs to be recoated, so that coating material must subsequently be removed from the diffuser region in the through-hole.
U.S. Pat. No. 4,743,462 discloses a method for closing a film cooling hole, in which a plug consisting of a pin and a spherical head is inserted into the film cooling hole. A bell-shaped indentation is thereby produced inside the coating. The indentation does not serve as a diffuser, however, since it is symmetrically designed.
The functionality of the head furthermore consists in the material of the head evaporating during the coating. It is not therefore possible to produce accurate, reproducible indentations for a multiplicity of film cooling holes.
Similar symmetrical widening of a film cooling hole is disclosed in FIG. 3 of U.S. Pat. No. 6,573,474.
EP 1 350 860 A1 discloses a method for masking a film cooling hole. The material of the masking means is selected so that no coating material is deposited there during the subsequent coating. An accurate, reproducible shape of the indentations inside a layer cannot be produced in this case. Furthermore, a diffuser is not described here.
EP 1 091 090 A2 discloses a film cooling hole in which a groove is made in the layer, so that the groove extends along a plurality of film cooling holes. Neither the film cooling holes nor the groove have a diffuser region.
U.S. Pat. No. 5,941,686 discloses a layer system, in which the substrate is processed. A diffuser region is not disclosed.
EP 1 076 107 A1 discloses a method for masking film cooling holes in which a plug, which protrudes from the hole, is respectively produced in the film cooling hole. To this end air is blown through the film cooling hole in a first step and a coating is applied, a precursor for the plug to be produced subsequently being introduced into the film cooling hole and into the coating. That part of the plug which is arranged inside the temporary layer has its shape determined by how strongly a medium is blown through the film cooling hole and how the coating of the temporary layer is carried out. The shape of that part of the plug which protrudes from the hole is therefore not reproducible.